Pedestrian-vehicle impact events are unfortunate but known occurrences. It is known that in a pedestrian collision thirty-seven percent of injuries were suffered by lower extremities. (Crandall et al., “Designing Road Vehicles for Pedestrian Protection,” BMJ [formerly British Medical Journal], 324 [7346], pp. 1145-1148), May 11, 2002.)
The front edge of the vehicle hood is typically a relatively stiff area that impacts an adult's upper leg during a pedestrian-vehicle impact event. The vehicle front and specifically the front overhang are designed to identify vehicle class and model type. In the case of the modern sports car, the front end is typically designed such that the vehicle has an overall low profile and a large hood to accommodate a high-power engine and matching powertrain. The front overhang of regular sedans and sports utility vehicles is designed to be stiff enough so that damage to the front end during a low speed crash is minimal. Larger vehicles, such as trucks, are often designed to enhance the sizes of the vehicle's grille and engine compartment, thus exaggerating the appearance of power and aggressiveness. In most of these cases the design aspects present challenges to the pedestrian during a collision.
The kinematics of a pedestrian during an impact depends on the characteristics of the vehicle front, its speed and the size of the pedestrian. If the center of gravity of a standing or walking pedestrian is higher than the leading edge of the vehicle then the pedestrian's body may at least partially wrap around the vehicle front or may be lifted into the air. The former is the most common result where the center of gravity is higher than the leading edge of the vehicle while the latter is the most common result in a high speed impact.
In the circumstance where an adult pedestrian at least partially wraps round the vehicle front it is the pedestrian's upper leg that is impacted by the edge of the hood causing injury to the upper leg. If the impact event involves a child then the child's head or other body parts could be impacted upon the edge of the hood causing serious injury.
Recognizing this risk of injury to pedestrians, according to the European New Car Assessment Programme (“Euro NCAP”), to achieve a five-star rating, all vehicles will need to be equipped with a pre-crash sensing system called Autonomous Emergency Braking (AEB) by 2014 and with pedestrian recognition system by 2016. Additionally, Euro NCAP phase-in star rating requirements put more emphasis on pedestrian protection which includes a pedestrian's upper leg.
In the United States, the National Highway Traffic Safety Administration is planning to introduce similar regulatory framework for pedestrian protection starting in 2016. Accordingly, global auto manufacturers urgently need new technologies to design front end of the vehicles to minimize injuries to pedestrian and to achieve highest possible safety ranking by regulatory agencies.
New pedestrian technologies can benefit from using signal from existing Autonomous Emergency Braking (AEB) systems with pedestrian detection. Based on that signal, technology countermeasures can be deployed to reduce injuries to pedestrians.
Such pre-crash sensing system for pedestrian detection may not need to be 100% reliable. In the event of a false positive signal resulting in a false deployment, the pedestrian technology can be reset to non-deployed state automatically after a pre-determined time delay and be available for next use case.
Known tests, such as the EuroNCAP pedestrian protection test protocol, includes measures to protect the upper leg from impacting the hood (or bonnet) leading edge (“BLE”). The challenge in this test is that the impact velocity, angle as well as impact kinetic energy (KE) and legform mass are determined by look-up diagrams in the test protocol. Employed standards are based on the bonnet leading edge height (“BLEH”) and the bumper lead (“BL”) of the target vehicle at the impact location. The styling of a vehicle is determined at an early stage of a vehicle program which can result in a high initial KE level in the upper legform test.
A known countermeasure to meet known pedestrian protection requirements is to incorporate a deployable hood into the vehicle. However, while providing arguable improvements in the state of the art, some deployable hood designs do not result in satisfactory pedestrian protection at the front of the vehicle.
Accordingly, there is a need for a practical and effective system to protect the upper leg of a pedestrian in a pedestrian-vehicle impact event. As in so many areas of vehicle technology there is always room for improvement related to the protection of pedestrians in a pedestrian-vehicle impact event.